The present invention relates to a predictive analysis method and a predictive analysis system for predicting engine performance through analysis of movement of a working fluid by using CFD (Computational Fluid Dynamics) and a control program for use in the predictive analysis method and system.
In order to evaluate the performance of an engine, a transmission or the like, a variety of measurement and test methods have been conventionally proposed as disclosed in, for example, Patent Document 1 (National Publication of translated version No. 2002-526762). Also, Patent Document 2 (Japanese Laid-Open Patent Publication No. 2002-148147) discloses a simulation system capable of evaluating the performance of a power train before completing the development of an engine.
As a technique for such a simulation, the performance of an engine is generally predicted on the basis of the result of a movement analysis of an intake gas or a combustion gas, that is, a working fluid, through application of the CFD. Specifically, a virtual experiment (simulation) for simulating, for example, a complicated flow of an intake gas sucked from an intake port into a combustion chamber through numerical calculation using a computer, and, for example, the shape of the intake port is determined on the basis of the result of the simulation. Thus, the number of development man-hour spent on trial manufacture and repeated experiments can be reduced so as to realize efficient design and development.
In particular, owing to recent remarkable improvement of calculation capabilities of a computer, a complicated shape of an intake port or the like and a flow of an intake gas within the intake port can be three dimensionally simulated. Therefore, there is no need to actually experimentally manufacture an engine in order to predict change of flowing resistance of the intake gas or volumetric efficiency of a cylinder caused by changing the shape of the intake port.
However, there is no simulation system capable of three dimensional simulation of all the flows of an intake gas and an exhaust gas involved in the running of an engine. This is because, no matter how much the calculation capabilities of a computer has been improved, it is unrealistic to three dimensionally simulate all of the shapes of intake gas passages different among respective cylinders of a multi-cylinder engine, the states of gas exchange in combustion chambers and flows of a burnt gas blowing out from each combustion chamber to an exhaust system.
Accordingly, in the case where the whole performances (such as an output, drivability and emission) of an engine are to be predicted, for example, experiment data obtained by examining various performance characteristics of the engine is accumulated so as to construct a database in which these performance characteristics are statistically correlated with one another. Also, simulation is performed by using a simple physical model for simulating a flow of an intake gas or an exhaust gas as a one dimensional flow. Thus, findings obtained on the basis of the database of the performance characteristics and the result of the one dimensional simulation are combined for predicting the performance of the engine.
Furthermore, in addition to the one dimensional simulation using the simple model, simulation for three dimensionally simulating, for example, an intake gas in an intake port alone is performed, and the results of these simulations are combined so as to improve the accuracy of the analysis. However, a CFD analysis program for such a three dimensional flow is generally difficult to deal with, and a large number of know-how is necessary for the setting for improving the accuracy. Therefore, a burden of a specialized analysis expert is increased, so that the development may be delayed due to insufficient manpower.
In consideration of this problem, the present inventors have developed a system in which a simple physical model for simulating the whole operation of an engine by using one dimensional movement of a working fluid (i.e., a flow of an intake/exhaust gas) as described above is used and merely a part of the physical model can be replaced with a three dimensional model for a CFD operation. Also, in this system, a user-friendly interface is employed and complicated setting peculiar to a three-dimensional CFD analysis program is automated, so that the system can be easily dealt with by any person that is not a specialized analysis expert.
However, even when the flow of the working fluid in merely a part of the engine is simulated as a three dimensional flow as in the aforementioned system, the computational complexity is still large, and hence, it is difficult to obtain the analysis result within a practical time at desired accuracy. Specifically, for example, in a four-cycle four-cylinder engine, in the case where a model for simulating a flow of the intake gas from a surge tank to the inlet of each independent intake gas passage as a three dimensional flow and simulating the other flows as one dimensional flows (see FIG. 3) is used, it is actually necessary to simulate the flow from the surge tank to the independent intake gas passage as the three dimensional flow merely when the corresponding cylinder is in an intake process. Accordingly, if the CFD operation using the one and three dimensional complex model is performed over the whole combustion cycle of the engine, the operation includes a large number of unnecessary calculations, which means that there is room for increasing the operation speed.
The present invention was devised in consideration of the aforementioned disadvantages, and an object is, in analysis of the movement of a working fluid of an engine through application of the CFD, improving the utility as a design/development tool by reducing time required for the CFD operation as much as possible with the analysis accuracy kept sufficiently high.